In production of semiconductor devices, an electron beam exposure technique receives a great deal of attention as a promising candidate of lithography capable of micropattern exposure at a line width of 0.1 μm or less, and several electron beam exposure methods have been proposed. For example, a variable rectangular beam method draws a pattern with one stroke. This method suffers many problems as a mass-production exposure apparatus because of a low throughput. To increase the throughput, there is proposed a pattern projection method of reducing and transferring a pattern formed on a stencil mask. This method is advantageous to a simple repetitive pattern but disadvantageous to a random pattern such as a logic interconnection pattern in terms of the throughput, and a low productivity disables practical application.
To the contrary, a multi-beam system for drawing a pattern simultaneously with a plurality of electron beams without using any mask has been proposed. This multi-beam system is very advantageous to practical use because of the absence of physical mask formation and exchange. What is important in using multiple electron beams in the multi-beam system is the number of electron lens arrays used in this system. The number of beams is determined by the number of electron lens arrays which can be incorporated in an electron beam exposure apparatus, and is a main factor which determines the throughput. How to improve the lens performance while downsizing the lens and increasing the density is one of important factors for improving the performance of the multi-beam exposure apparatus.
Electron lenses are classified into electromagnetic and electrostatic types. The electrostatic electron lens does not require any coil core or the like, and is simpler in structure and more advantageous to downsizing than the electromagnetic electron lens. Typical prior arts concerning downsizing of the electrostatic electron lens (electrostatic lens) are as follows.
A. D. Feinerman et al. (J. Vac. Sci. Technol. A10(4), p. 611, 1992) disclose a method of anodically bonding a fiber and a V-groove formed by Si crystal anisotropic etching of an electrode fabricated by a micromechanical technique, thereby forming a three-dimensional structure from three electrodes serving as single electrostatic lenses. The Si film has a membrane frame, a membrane, and an aperture which is formed in the membrane and transmits an electron beam. K. Y. Lee et al. (J. Vac. Sci. Technol. B12(6), p. 3,425, 1994) disclose a structure obtained by bonding Si layers and Pyrex glass layers by using anodic bonding. This technique fabricates aligned microcolumn electron lenses. Sasaki (J. Vac. Sci. Technol. 19, p. 963, 1981) discloses an arrangement in which three electrodes having lens aperture arrays are arranged into an Einzel lens. In an electrostatic lens having this arrangement, a voltage is generally applied to the central one of three electrodes, and the remaining two lenses are grounded, obtaining lens action.
In the prior arts, an electron lens is constituted by stacking a plurality of electrodes via insulator members. The insulator member which constitutes the electron lens in the prior art is exposed to an electron beam, and is readily charged. That is, an electric field is generated by charges on the insulator surface. The electric field makes the electron beam orbit unstable or increases aberration, failing to focus a beam. This is so-called charge-up. As a measure against this problem, the insulator member is covered from a beam, preventing charge-up. However, this method can be applied to only a single-beam lens. Charge-up of the insulator member is still a serious problem in a multi-charged beam lens formed using a semiconductor process.
In combining electrodes into an electron lens in the prior arts, the method by Feinerman et al. and the method by Lee et al. newly require an anodic bonding apparatus in addition to a process apparatus for fabricating an electrode. The method by Sasaki does not clarify a method of combining electrodes into an electron lens.
When electrodes are bonded to downsize an electron lens, electrodes 1001 are fixed by an adhesive 1002 via insulator members 1005, as shown in FIG. 23. The adhesive 1002 is lower in dielectric breakdown voltage than the insulator member 1005, and dielectric breakdown may occur in the adhesive 1002, decreasing the operating voltage of the electrostatic lens.